This document discusses data flow diagrams (DFDs) and their elements. It explains that a DFD visually shows how data moves through an information system by using graphical symbols like processes, data stores, external entities, and data flows. It provides examples of a context diagram showing one overall process and all external entities, as well as a level 0 diagram breaking that process into major sub-processes and showing data flows between them. The document also outlines how DFDs can be further decomposed into level 1, 2, and additional diagrams to show internal processes and data flows in more detail.

1. Data Flow Diagram (DFD)
Prof. Sadique Nayeem

2. Reading a DFD

3. Elements of a DFD
• Process
– An activity or function performed for a specific
business reason
– Manual or computerized
• Data flow
– A single piece of data or a logical collection of data
– Always starts or ends at a process

4. Elements of a DFD
• Data Store
– A collection of data that is stored in some way
– Data flowing out is retrieved from the data store
– Data flowing in updates or is added to the data
store
• External entity
– A person, organization, or system that is external
to the system but interacts with it.

6. Context diagram
• First DFD in every business process.
• Shows the context into which the business process fits.
• Shows overall business process as just one process (process 0).
• Shows all the external entities that receive information from or
contribute information to the system.
• External entity
– Student
• Process
– Student Administration
process application
• Data Flows
– Application Form
– Confirmation/Rejection
Letter

7. Level 0 Diagram
• Shows all the major processes that comprise the overall
system – the internal components of process 0
• Shows how the major processes are interrelated by data flows
• Shows external entities and the major processes with which
they interact
• Adds data stores

8. Level 0 DFD

9. Level 0 DFD
• External entity
– Student
• Processes
– Check available, Enroll student, Confirm Registration
• Data Flows
– Application Form, Course Details, Course Enrolment Details,
Student Details,
– Confirmation/Rejection Letter
• Data Stores
– Courses, Students

10. Levels of DFD

11. Level 1 Diagrams
• Generally, one level 1 diagram is created for every major
process on the level 0 diagram.
• Shows all the internal processes that comprise a single
process on the level 0 diagram.
• Shows how information moves from and to each of these
processes.
• If a parent process is decomposed into, for example, three
child processes, these three child processes wholly and
completely make up the parent process.

12. Level 2 Diagrams
• Shows all processes that comprise a single process on the
level 1 diagram
• Shows how information moves from and to each of these
processes
• Level 2 diagrams may not be needed for all level 1 processes
• Correctly numbering each process helps the user understand
where the process fits into the overall system

14. Steps in Building DFDs
• Build the context diagram
• Create DFD fragments for each use case
• Organize DFD fragments into level 0 diagram
• Decompose level 0 processes into level 1 diagrams as needed;
decompose level 1 processes into level 2 diagrams as needed.
• Validate DFDs with user to ensure
• completeness and correctness

21. Reference
• Systems Analysis Design, 5th edition, A. Dennis, B. A. Wixom and R. M.
Roth, John Wiley and sons.